Films for ostomy applications should have good odor barrier properties and produce minimal noise when flexed or wrinked to avoid embarrassment to users. Typically, films currently in use for ostomy applications utilize polyvinylidene chloride (PVDC) or copolymers of vinylidene chloride with a comonomer such as methylacrylate or vinylchloride as the gas barrier layer of a multilayer film. Such multilayer films have good resistance to odor transmission and are also relatively quiet; however, they are also believed to be hazardous to the environment when disposed of by incineration, a common practice in numerous countries. Chlorinated polymers generate hydrochloric acid as a byproduct of incineration and are believed to be a significant contributor to hydrochloric acid release from incinerator flue gases. Furthermore, chlorinated polymers are believed to form toxic dioxin derivatives as byproducts of incineration which are retained in the ashes and may possibly cause solid waste disposal problems.
Unfortunately, films formed of chlorine-free barrier resins tend to be stiffer and noisier than films utilizing conventional PVDC-based resins and do not match the quality of conventional chlorinated films for use in ostomy appliances. Thus, a need exists for a multilayer film which is chlorine-free, can be manufactured by coextrusion from readily available raw materials, is heat sealable, has high softness and low noise when flexed or wrinkled, and is impermeable to fecal odors.
U.S. Pat. No. 5,567,489 discloses a multilayer barrier film in which a chlorine-free barrier layer is composed of amorphous nylon, crystalline nylon, copolymers of ethylene and vinyl alcohol, or blends thereof. Although data presented in the patent indicate the multilayer films to be comparable in quietness to some chlorinated films in general commercial use, experience has revealed that such chlorine-free films are nevertheless significantly noisier than the chlorine-containing films commonly employed for the fabrication of ostomy pouches. The general observation is that chlorine-free barrier resins are high modulus, stiff materials that do not lend themselves to the production of low noise ostomy films. This is true of all nylon (polyamide) barrier resins, both crystalline and amorphous. It is true also of other known chlorine-free barrier resins such as hydrolyzed ethylene-vinylacetate copolymers, commonly known as ethylene-vinylalcohol copolymers, and copolymers of acrylontrile or methacrylontrile of high nitrile content, commonly known as nitrile resins.
Other references illustrating the current state of the art relating to chlorine-free multilayer films are U.S. Pat. Nos. 5,496,295, 5,643,375, and 5,407,713.
One aspect of this invention lies in the discovery that if a chlorine-free multilayer film is composed of polyester resin coextruded with at least one skin layer, preferably two such skin layers, of a homopolymer of ethylene or copolymer with alpha-olefin or ester-containing comonomer, the resulting multilayer film is of relatively low modulus and exhibits low noise upon flexing. The polyester resin barrier layer, although having limited oxygen permeability, is highly effective as an odor barrier, thereby resulting in a multilayer film particularly suitable for the fabrication of ostomy pouches. The polyester resin of choice is polyethylene terephthalate, and the skin layers are composed of a copolymer of ethylene and an ester-containing monomer such as methyl acrylate, ethyl acrylate, butyl acrylate or vinyl acetate. While the skin layers and barrier layer may be coextruded in direct contact with each other, it has been found that the interlaminar strength of the film may be significantly increased by interposing adhesive tie layers between the skin layers and barrier layer. Each such tie layer may be an ethylene copolymer with reactive functional groups, such as an anhydride modified copolymer of ethylene and an acrylic or methacrylic ester.
In addition to being heat-sealable and having exceptional odor-barrier properties, the multilayer films of this invention are relatively soft (have low modulus) and are superior in quietness to known chlorine-free films in which the odor-barrier layers are formed entirely of nylon, ethylene-vinylalcohol copolymers, or nitrile resins. With regard to the generation of noise upon flexing, the chlorine-free multilayer films of this invention compare favorably with prior art ostomy films having chlorinated barrier layers. A pouch formed of the multilayer film of this invention therefore has properties comparable to those exhibited by high-quality pouches formed of chlorine-containing compositions but without the environmental shortcomings described above.
Other features, advantages and objects of the invention will become apparent from the specification and drawings.